Conventionally, in a lithographic process for manufacturing a semiconductor device, liquid crystal display device and so forth, an exposure apparatus has been used. In such an exposure apparatus, patterns formed on a mask or reticle (to be genetically referred to as a “reticle” hereinafter) are transferred through a projection optical system onto a substrate such as a wafer or glass plate (to be referred to as a “substrate or wafer” herein after, as needed) coated with a resist or the like.
In general, the semiconductor device is manufactured by using the exposure apparatus, and it is composed of a plurality of circuit pattern layers on a wafer. Therefore, the positioning of the shot area on the wafer and the reticle (to be referred to as “alignment” hereinafter) must be precisely performed when they are overlaid in the exposure apparatus. In order to position them in the apparatus precisely, the position of the wafer must be detected correctly, and the techniques, for example, disclosed in the publication of Japanese unexamined patent application (refer to as “Japan laid-open”, hereinafter) No. H9-92591, have been proposed.
In such conventional position detecting methods, enhanced global alignment (to be referred to as “EGA” hereinafter) is widely employed. In EGA, fine alignment marks, which are positioning marks transferred together with circuit patterns on the wafer, are measured at a plurality of positions within the wafer, in order to precisely detect positional relations of the reference coordinate system and the arrangement coordinate system (to be referred to as “wafer coordinate system” hereinafter). Wherein, the reference coordinate system defines the movement of the wafer, and the arrangement coordinate system defines the arrangement of the respective shot areas on the wafer. The arrangement coordinate of the respective shot areas are then obtained by the least-squares approximation or the like, and stepping is performed by using the calculated result in accordance with the accuracy of the wafer stage on exposure. EGA is disclosed in, for example, Japan laid-open No. S61-44429 and its corresponding U.S. Pat. No. 4,780,617. In order to use such EGA, the fine alignment mark formed on the predetermined position on the wafer is observed by high magnifying power. However, the observation field is essentially narrow under the observation with high magnifying power. Therefore, prior to perform fine alignment, the following detection for the reference coordinate system and the arrangement coordinate system is preformed to catch fine alignment marks certainly within the narrow observation field.
At first, the outer edge of the wafer, an object in the positioning detection, is observed. The positional relation between the reference coordinate system and the arrangement coordinate system are detected in the predetermined accuracy derived from the position of the notch in the outer edge, the position of the orientation flat or the outer edge of the wafer. This detection procedure is referred to as “rough alignment”.
Then, the observation apparatus is moved to the wafer or vice versa, that is, relative movement of the observation apparatus and the wafer according to the positional relations of the first approximation arrangement coordinate system obtained by rough alignment and the reference coordinate system. A plurality of search alignment marks is caught within the relatively wider observation field, and the search alignment marks are observed. Based on the search alignment marks observed as mentioned above, the positional relation between the reference coordinate system and the arrangement coordinate system is detected in higher accuracy than that obtained in the rough alignment. Such detection procedure is referred to as “search alignment” hereinafter. The observation field of the observation unit is set in an enough range to catch the search alignment mark when the inaccuracy is included in the positional relation between the reference coordinate system and the arrangement coordinate system detected in the rough alignment. Further, the accuracy for the detection of the positional relation between the reference coordinate system and the arrangement coordinate system is set in an enough range for the fine alignment performed in next.
As mentioned above, the rough alignment and the search alignment are sequentially performed. Then, the wafer is moved against the observation unit or vise versa, according to the positional relation between the reference coordinate system and the second-approximated arrangement coordinate system, which is obtained in the search alignment. After that, a plurality of fine alignment marks on the wafer is caught in a narrow observation field to perform fine alignment.
In conventional position detecting methods, three alignments such as rough alignment, search alignment and fine alignment are sequentially conducted. Among them, both in the search alignment and rough alignment, the positions of a plurality of marks to be observed must be detected after they are caught in the observation field, wherein the wafer is moved to the observation unit or vise versa. Therefore, it takes much time to detect the positions of the shot areas by using the conventional method.
On the other hand, in the exposure apparatus, high through put is needed because this apparatus is employed for mass production of semiconductor devices. Therefore, the alignment procedure composed of three steps as mentioned above becomes a problem on the way to accomplish the high through put. Accordingly, it is expected that the new technology to shorten the alignment time, maintaining the present accuracy of the alignment.
The present invention has been made in consideration of the above-mentioned situation. The first object of the present invention is to provide the position detecting method and a position detecting apparatus to conduct the position detection with high accuracy in a short time.
The second object of the present invention is to provide the exposure method and the exposure apparatus with high accuracy and high through put depending on the rapid and precise position detection.
The third object of the present invention is to provide the device on which fine patterns are precisely formed.